Is it a coating of special material for hardening?
Bentley manual says lap only on exhaust valves.

When I lapped my exhaust valves in my recent engine
rebuild, I remember I could hardly remove anything.
But the valve seats did show a gray surface indicating
removal of some metal.

Using a magnifier I could see very fine pitting (very small
dots) randomly spread over the entire exhause valve surface.
I tried to lap them off but they remained as was. I left
them alone. Those pitting were very small dots. They did
not affect sealing negatively in any way.

BTW, I have had 2000 miles on my rebuilt engine after my Yosemite
trip. I am much happier now from the engine's performace.
Most likely I won't need to do anything to it again.
It is able to accelerate reasonably fast now. I think another
2 k miles later it will be a champ. Benny was right that I
just need more break-in for the piston liners.

David

--- Mike <mbucchino@CHARTER.NET> wrote:

>   The reason VW says not to grind exhaust valves, is due to a surface
> hardening process that is ruined by grinding.  Intake valves don't have this
> same treatment, and as such are OK to re-grind.
>   Any good VW rebuilder knows this, and heeds the factory's advice to
> prevent exhaust valve failures (ie; shortened life).  They do a good enough
> job failing on thier own without this added assistance.......
>
> Mike B.
>
> ----- Original Message -----
> From: "Evan Mac Donald" <macdonald1987@SBCGLOBAL.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Friday, July 06, 2007 11:41 AM
> Subject: Re: exhaust valve grinding
>
>
> > As long as the minimum thickness at the edge of the valve is not violated,
> > nothing bad. My brother did the machine work on the heads of my 1.9l about
> > 140k miles ago. Nothing bad has come of grinding the exhausts. Now, he did
> > take minimal cuts on all the valves - just enough to get a straight seat.
> > We did that on the valves and on the heads. It amounted to just a little
> > more than a "hard" lapping, IIRC. Not alot needed to be done. I was glad
> > for that, because exhaust valves are the very devil to lap by hand,
> > because they are such a hard metal. BTDT!
> >
> > "Giasson, Pascal (DNR/MRN)" <Pascal.Giasson@GNB.CA> wrote:  I just got a
> > valve job done on my 1.9 heads from a machine shop. I gave
> > them the Bentley and showed them where it says not to grind the exhaust
> > valves. They said they have reground exhaust valves many times for the
> > local VW mechanic and this was the first time they were made aware that
> > VW says not to grind them. I thought they were just going to lap them
> > as per the Bentley, but the machinist said they needed to be ground so
> > that is what he did. Does anyone know what will happen to a ground
> > exhaust valve? Thanks
> >
> >
> >
> > Pascal
> >
> > '84 Westy
> >
>

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